1. Field of the Invention
The present invention relates to chemical mechanical polishing (CMP), and more particularly, to a conditioner and a conditioning disk for conditioning a CMP pad, and a method of fabricating, reworking, and cleaning the conditioning disk.
2. Background of the Related Art
Highly integrated semiconductor devices require a sophisticated pattern formation technique, and use a multilayer structure for circuit distribution. This means that the surface structure of these semiconductor devices is more complicated, and step height differences between intermediary layers are more severe.
These step height differences cause many process failures in the semiconductor device fabrication process, for example, in the photolithography process for forming a photoresist pattern on a semiconductor wafer, which comprises the steps of coating the wafer with photoresist, aligning a mask having circuit patterns with the wafer having photoresist thereon, and performing an exposure process and a development process.
In the past, the formation method for precise patterns was easier, because the critical dimension (CD) of the pattern was relatively wide, and the semiconductor devices had fewer structural layers. However, the step height difference is increasing due to the finer patterns and multilayered structure of the modem devices. Therefore, it is more difficult to focus between the upper and the lower position of the step height during the exposure process, and it is also difficult to obtain more precise patterns.
Therefore, in order to reduce the step height difference, a planarization technique for the wafer has become important. A planarization technique such as SOG (Spin On Glass) film deposition has been introduced, or a partial planarization technique, such as etch back or reflow, etc., has been used, but many problems persist. Accordingly, a CMP (chemical mechanical polishing) technique for global planarization has been introduced, wherein the planarization is performed throughout the whole surface of the wafer.
The CMP technique planarizes the wafer surface through both chemical and mechanical reactions, whereby the protrusions existing on the surface of the thin film on the wafer chemically react with a slurry supplied to the wafer, with the surface of the wafer having the device pattern contacting a polishing pad surface. At the same time, the protrusions are planarized mechanically by rotation of a polishing table and the wafer.
Referring to FIGS. 1 and 2, the CMP apparatus 1 comprises a polishing table 10 having a polishing pad 12 made of polyurethane attached thereon, a wafer carrier 20 for fixing and rotating a wafer 16, with the thin film pattern 18 on the wafer 16 contacting the polishing pad 12, a slurry 14 supplied on the polishing pad 12, and a conditioner 22 displaced on the opposite side of the wafer carrier 20 and having a conditioning disk 24 attached thereon for conditioning the polishing pad 12.
In the CMP technique using the CMP apparatus 1, removal rate and planarization uniformity are very important, and these are determined by process conditions of the CMP apparatus 1, and the type of slurry 14 and polishing pad 12 used. In particular, the polishing pad 12 affects the removal rate, which should be properly maintained within a process specification by monitoring the surface state of the conditioning disk 24 of the conditioner 22 which conditions the polishing pad 12, and replacing the conditioning disk 24 when necessary.
Referring to FIG. 3, the conditioning disk 24 has artificial diamonds 26 attached to its surface by a nickel thin film used as an adhesive film 25, and the artificial diamond 26 abrades the surface of the polishing pad 12 which is made of polyurethane and has fine protrusions 27.
While the CMP process is continuously being performed for the wafer 16 on the polishing pad 12 by the supplied slurry 14, by-products 28 entrained in the slurry 14 are deposited between the protrusions 27.
Therefore, the surface of the polishing pad 12 becomes slippery with repeated CMP processing, thereby abruptly decreasing the removal rate for subsequent wafers. In order to restore the required removal rate, and maintain the condition of the polishing pad 12, a conditioning is performed to remove the by-products 28. The conditioning is performed by first placing the conditioning disk 24 with the artificial diamond 26 into contact with the surface of the polishing pad 12, and then, rotating the conditioning disk 24 at a certain speed so as to increase the roughness of the polishing pad 12. Therefore, the film of each wafer planarized during the CMP process is within a certain specification.
The conditioning method for the polishing pad 12 is different for a metallic film CMP than for an oxide film CMP. In the case of metallic film CMP, the conditioner 22 conditions the surface of the polishing pad 12 after the CMP for a wafer is preformed. For the oxide film, the CMP process is carried out by simultaneously performing the conditioning of the polishing pad 12 by the conditioner 22 and the CMP for the wafer.
Referring to FIGS. 4 and 5, the conditioning disk 24 has artificial diamonds 26 of a certain size attached on its surface with a nickel thin film 25 functioning as the adhesive. With the continuously-carried out CMP, the by-product 28 including the slurry 14 also accumulates between the artificial diamonds 26 on the conditioning disk 24 as well as on the polishing pad 12. The abrasion of the artificial diamonds 26 itself as well as the accumulation of the by-products 28 between the artificial diamonds 26 decreases the efficiency of the conditioning for the polishing pad 12.
That is, the conditioning effect of the conditioning disk 24 on the polishing pad 12 changes according to the state of the artificial diamonds 26 on the conditioning disk 24.
The size of the artificial diamonds 26 is approximately 68 .mu.m, with approximately 30 to 40 .mu.m protruding from the nickel thin film 25. As a result, the conditioning disk 24 has a short life time, and frequent replacement of the conditioning disk 24 results in decreased productivity and deterioration of production yield due to increased process failures.